Apparatus for mine roof control



Aug.- 18, 1959 J. F. JOY

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United States Patent APPARATUS FOR MNE ROOF CONTROL Joseph F. Joy,Pittsburgh, Pa., assignor to Joy Manufacturing Company, Pittsburgh, Pa.,.a corporation of Pennsylvania Original application May 1, 1948, SerialNo. 24,574, now Patent No. 2,714 505, dated August 2 1955. Divided andthis application July 27, 1955, Serial No. 524,904

Claims. (Cl. 61-45) My invention relates to apparatus for mine roofcontrol, and more particularly to apparatus particularly adapted to roofcontrol immediately back of a working face.

This application is a division of my application, Serial No. 24,574, ledMay 1, 1948, now matured into Patent No. 2,714,505.

Roof control has heretofore been one of the most expensive, as well astroublesome, items with respect to mining. This is true because of theexpense of the materials used, such as timbers, steel, brick, etc., andbecause so much of the materials used is lost as a result of roofsubsidence as the working face advances. It is also true because of thelarge amount of labor involved in building cribs, setting timbers, etc.Accordingly the provision of an effective and rapidly adjustable meansfor effecting roof control, and one that is relatively secure againstloss of its elements and which can be used many times, is a highlydesirable thing. This is particularly so with the present tendency toincrease the length of Working faces, but it is not without its benefitseven with short faces such as are common in room and pillar mining.

The present invention is in no sense limited to such a system, but itsunderstanding may be facilitated by considering its application to anadvancing system of longwall mining, Under this system, a working faceis opened up and advanced into the solid seam away from the mine shaftor opening. Roadways leading to each end of the longwall face must bemaintained open, both to aiford openings of suicient cross` section forthe requisite air circulation and to permit the transportation of coalfrom the productive face. These roadways are held open by roadway packwalls-permanent rock cribs so ruggedly constructed that the roadwaysvvill not be blocked as the result of roof subsidence. Between theroadway pack Walls, and immediately to the rear oif the working face,timber in the form of upright posts, and, just back of the posts, woodenor steel cribs are commonly provided to support the roof. Just back ofthe cribs, either partial or complete caving may be expected to occur.When the partial caving system is used, intermediate rock packs arelocated at regular intervals between the roadway packs, with the roofbeing permitted to subside, between the various pack walls, along theface. In the complete caving system, the strata overlying the mined outarea opposite the face are permitted to cave in completely, irl theareas between the roadway packs, except for the strip or space adjacentthe face used for mining and working purposes.

Particularly with the system last mentioned it is important to resistroof subsidence immediately back of the longwall face, and to preventsubsidence or the like except along more or less denite lines in arelatively predetermined space relation to the face as the latteradvances. Such a fracture line should be several feet (perhaps a dozen)back from the face, and this can not be .certainly accomplished, evenwith the use of cribs as "ice well as posts, with conventional methods;and, Iwith such arrangements, losses of roof supporting timber arefrequent, and at times the fracture line may get too close to the coalface, with resultant expense and time consuming labor.

It will be understood that when the roof commences to subside, the rockordinarily breaks and falls in fragments or" various sizes until thespace between the bottom and the roof is completely filled, due to thefact that the broken rock occupies more space than the solid, and theroof is again supported. In some cases the bottom may heave, in additionto subsidence of the roof occurring, in which event the roof and bottommay converge towards a plane below the one and above the other.

It will be understood that in the absence of adequate control, therewill be a convergence of the roof and bottom to a more or less degreeimmediately back of the coal face, and, the Wider the face, the morerapidly this convergence may be expected to occur. This convergence isthe natural result of the tremendous forces tending to close the spaceresulting from the removal of the coal seam, and, if the convergence betoo inadequately resisted, a fracture of the roof at the coal line islikely to result, interfering greatly with the ordinary production otcoal from the working face. With means such as I have provided in mypresent invention, it is theoretically possible to have the rooffracture just to the rear of the improved roof jacks, but of course theactual composition of the roof and iloor strata will affect the results.For example, when fire clay, relatively soft shales or slates liedirectly above the roof, there will be a great tendency to lill all ofthe space resulting from the coal removal, and when the floor is hard,the filling action may be due wholly to subsidence. This filling actionmay be due partially to subsidence and partly to floor heaving, when thefloor is not rigid.

In any event, it is important to provide equipment that will meetconditions (a) Where a relatively sharp break may occur just to the rearof the jack devices arranged more remote from the face, (b) where thereis a mutual gradual approach between the oor and the roof outwardly ofthe jacks, perhaps partially under direct control of the outer jacks,and (c) where there is approach of but one of the initially generallyhorizontal boundaries towards the other.

The principal object of this invention is to provide an improved anddependable means for resisting the closing of the gap caused in theearths strata by the removal of certain layers thereof such as coalseams or the like, for the required length of time to permit the miningof said layers. A more specific object is to provide an improved roofsupporting structure having means incorporated therein for facilitatingits being progressively advanced along with the advance of a mine face,and desirably with but slight or no release of the resistance to roofsubsidence. Another object is to provide an improved roof jackmechanism-one which shall permit jack adjustment without interruption ofroof support. Another object is to provide an improved roof jackmechanism incorporating improved roof vand loor engaging devices. Afurther object is to provide an improved roof jack mechanismincorporating spaced roof supporting jack devices and an intermediateabutment jack device. Other objects and advantages of the invention willhereinafter more fully appear.

ln the accompanying drawings, in which two illustrative embodimentswhich my invention may assume in practice have been shown for purposesof illustration,

Fig. l is a plan view, and Fig. 2 a sectional view taken on the plane 22 of Fig. 1, with parts shown in elevation of an illustrative embodimentof my improved roof Controlling apparatusI v Fig. 3 is a verticalsectional view showing on an enlarged scale details of construction ofthe adjusting cylinder and piston mechanism kand of the jacks forming apart of the structure illustrated in Figs. 1 and 2.

Fig. 4 is a sectional View showing a control valve mechanism for thestructure of Figs. 1, 2 and 3.

Fig. 5 is a view with parts shown in elevation showing a modificationwhich the invention may assume in practice. Fig. 6 is a view partiallyin elevation and partially in section showing a control valve mechanismappropriate to the control of the apparatus of Fig. 5.

For the purpose of maintaining as effectively as possible a support forthe roof and for avoiding the necessity for reducing the roof supportduring jack movement, I have illustrated in Figs. l, 2 and 3, a form ofmy invention which is intended to permit jack movement without relief ofthe pressure of the jacks which are sustaining the load of the mineroof; and I do this by providing a jack which provides a firm abutmentagainst which thrust can be exerted to effect movement of the roofsupporting jacks, that is those jacks which have as their primaryfunction roof support, and by relieving of pressure, to the necessaryextent, the abutment providing jack when occasion exists for moving thislatter jack lforwardly to a new position. In this form all contacts,except in the case of the abutment jack, between the mine bottom and thejack structures and the mine roof and the jack structures is throughapparatus which will not require sliding of mine roof and floor engagingmeans against a serious frictional resistance. In other words, Iprovide, as parts of the floor engaging and of the roof engaging deviceswhich are to transmit the forces to the oor and to the roof, trackwaysupon which roller supported shoes are mounted, these trackways beingmade desirably of I-beam construction, with the flanges carried aroundsemi-circles at the ends, with trackway engaging rollers supported onthe pintles which connect floor and roof engaging, tread formingelements, and with the tread forming elements formed of simple shoe-likeconstruction with side projections to keep them from slipping laterallyotf the flange portions of the I-beam trackways.

of frames which are associated with each of the roof supporting jacks sothat there may be free pivoting about transverse horizontal axes in thecase of the lower elements and, with respect to the upper elements,there may be, not only a longitudinal rocking possible, but also alateral capacity for adjustment so that if the roof is not completelyflat (that is not completely parallel to the mine bottom) this will notprevent the effective use of the jack structures. By providing `anarrangement in which the forward jack (at least preferably the forwardjack) is prevented from movement out of vertical positions by reason ofthe nature of its extensible connection with the abutment jack and byconnecting the forward and rearward oor and roof engaging structureswith each other as later described, a very effective arrangement, proofagainst any possible collapse under the roof pressure, but yet capableof some yielding in the event that the burden of the roof is excessiveat a substantial distance from the face, ywill be made available.

We may now note the structure in mo-re detail. Since, except in thematter of length, the structure of all of the devices for transmittingpressure to the oor or to the roof is essentially the same, it willsuice to describe a single one of these in detail; and accordingly therewill be described the upper right hand (looking toward the face)roof-engaging element which is designated 16). This includes anelongated frame element 161 of rigid construction and consisting of acentral vertical ange 162 having top and bottom flanges 163 and 164which are joined bythe semi-circular flange portions 165 at the ends ofthe vertical ange 162. About the periphery of the elongated frameelement 161 there are ,adapted to travel a considerable number of tread,orshoe `elements Cil Desirably, I may provide connections'between theupper and lower pairs 166, which are connected together by pintles 167,which are surrounded by suitably hardened rollers 168, which roll on theanges 163, 164, 165. The shoe elements 166 are of squared U-shape incross section, and they have overlapping ear portions as may be seen at169, and they have inwardly projecting points 170 adapted to engage thesides of the peripheral flanges 163, 164, 165 and to prevent the lateralmovement of the shoes off of the anges. It will be vevident Vthat thisconstruction provides relatively long horizontal surfaces built up of amultiplicity of shoe elements for engagement, in the particular casedescribed, with the mine roof; and the other similar elements, bothroof-engaging and floorengaging, provide a similarly effectiveengagement with the surfaces which they contact which permits thetransmission of relatively large forces, though not too large forces,per square inch of contact, and yet permits, under longitudinallyapplied moving forces-furnished by means shortly to be described-therebeing effected bodily movement of the oor and roof engaging devicestoward the face without having to reduce the pressure which exists inthe jack cylinders which will also shortly be described. One thing moremight be added at this point, and that is the fact that forwardadjustment toward the face will be possible the more readily with thisapparatus because the roof and the floor will tend to become closer toeach other progressively as the distance from the face is increased.Theoretically, at least, it is possible that the cylinder and pistonmechanisms may actually have to be used to hold back advance, theabutment jack being xed in position and the iiuid entrapped within thecylinder and piston mechanism extending from said jack to the forwardjack being placed under pressure by the action of the pressures of theroof (or :roof and oofr) on the members which engage them.

Referring to Fig. l, it will be noted that at opposite sides of theflange 162 there are mounted plates 171 and 172 each formed with abearing collar 173, and it will be noted that these plates 171 and 172are bolted to the element 161 as at 174, and that the flange 162 has abore through it at 175 in alinement with the bores of the bearingcollars 173. There is arranged similar :structure in the case of allfour top or roof engaging structures 160, and likewise in the case ofthe four mine bottom engaging structures 176. Between the pairs of roofengaging structures there are extended cross frames 177 and 178, each ofthese having bearing pins 179 received in the bearing sleeves 173carried by the roof engaging elements 160 with which they areassociated. Each of the frames 177 and 178 is provided with a boxlikecenter portion 179 having a depending projection 180 curved like aportion of the surface of a ball or sphere and seating in acorrespondingly shaped socket or recess 181 formed in a top member 182carried by the piston structure 183 of the roof jacks which arerespectively involved. To distinguish these jacks for furtherdiscussion, the forward roof jack, whose piston structure 183 supportsthe cross arm 177, will be designated 184, and the rear roof jack will=be designated 185. There is also a cylinder member 186, in the case ofthe forward jack, and 187, in the case of the rearward jack. Thesecylinder members are mounted in cup-shaped portions 188 of cross frames189 and 190 which carry pivot pins 191 and 192 respectively, by whichthey are pivotally connected to the floor engaging structures 176. Thuseach oor structure is capable of some adjustment about horizontaltransverse axes but not about longitudinally extending axes as ispossible with the roof engaging structures 160. Since the rearward iioorand roof engaging element should be permitted to undergo adjustmentsrelative to the forward ones with which they make up pairs, but sincethe rearward elements have no means for advancing them except as theymay be furnished with traction by the forward elements, suitableconnections for electing such traction without interfering withindeasoaaoo pendent adjustments is provided. These may assume variousforms, but perhaps the easiest method is simply to provide chains 193 toconnect the cross members by which the various floor and roof engagingelements are individually supported. For example, the transverse members177 and 178 may be connected by pairs of chains 193, one chain at eachside of the intermediate abutment providing a jack structure laterdescribed and, similarly, pairs of chains may connect the cross armswhich rest at their opposite ends in the frames of the oor engagingstructures, the latter chains being numbered 194.

Devices similar to the devices 160 and 176 are connected pivotally at197 to the rear ends of the rearward roof engaging elements 160 and haveheavy wheels 198 journaled on axles 199 at their lower rearward ends,and are adapted, in the event that the roof starts to collapse, tosustain the weight of the roof and to derive from the weight of the roofa thrust towards the face so that the roof will not pinch the apparatusin such a manner as to prevent its forward movement.

The adjacent ends of each pair of oor and roof engaging members will beprovided with bumpers 200, as shown in Figs. l and 2, to preventinterference of the treads with each other in the event that, due tochanging angular relations of the roof and floor to each other, there bea tendency of one element to override the other. These bumpers will alsoserve to transmit the moving forces to the rearward jack device 185 andthe parts with which it is associated in the event that backing awayfrom the face becomes desirable as will be frequently the case after theends of shut-down periods, during which periods in some cases the entireroof supporting device will be moved just as close as possible to theface. It will also be possible to unhook the chains 193 and 194, andmove up only the forward jack during a shut-down period.

The means for effecting movement of the roof jacks of this embodiment ofthe invention includes an expansible and collapsible hydraulic abutmentjack device 201 which comprises a roof engaging pad 202 carried at theend of a piston structure 203, which is received in a cylinder structure204 into which iluid pressure can be supplied to effect a firmengagement of a base pad 205 with the mine bottom and the roof pad 202with the mine roof. This abutment jack has rigidly connected to it thepiston mechanism of a hydraulically extensible and contractable cylinderand piston mechanism 207 whose potential feeding range is desirably suchas to permit the effecting of an advance movement equal to the thicknessof the slice of coal which is to be removed. The cylinder and pistonmechanism 207 includes a piston rod 208 carrying a piston 209 which isreceived in the bore 210 of a cylinder 211 rigidly connected as at 212with the member 189. Suitable means is provided for delivering fluid tothe jack structure 201, to the jack 184, and to the jack 185, and alsoto the cylinder and piston mechanism 207; and a suitable valvearrangement for this purpose is shown in Fig. 4 and will later bedescribed.

It will be observed, in View of the rigid connection of the piston rod208 with the base of the abutment jack device 201 and the rigidconnection of the cylinder 211 of the cylinder and piston mechanism 207with the jack 184, that the extension of the jack 201 into iirm contactwith the mine roof and mine bottom will not only prevent the tipping ofthis jack but will also prevent the tipping of the jack 184 irrespectiveof any change in angular relation of the roof and oor engaging devices160 and 176 to the jack 184. The provision of the abutments 200 and ofthe chains 193 and 194 prevents the assump` tion by the rearward pair ofroof engaging devices 160 and floor engaging devices 176 of anypositions in which the jack 185 may be able to collapse by a swingingmovement. In summary, so long as the jack 201 remains erect,

there can be no collapsing of the jack mechanisms 184 or 18S exceptthrough opening of relief valves associated with them, or through thedeliberate venting of uid from; them. v

It will be evident, referring to the relative position of the partsshown in Fig. 2, that if the jack 201 be caused to exert pressurebetween the floor and the roof and if fluid be supplied to the bore 210of the cylinder 211 of the cylinder and piston mechanism 207 to the leftof the piston 209, the entire series of floor and roof engaging jackswill be moved toward the left in Fig. 2, that is, toward the face, andthis movement, except in the event that the roof pressure has becomeliterally terric-more than enough to cause the automatic Venting offluid from the jacks as hereinafter described-will be possible withoutany necessity for reduction in the pressure exerted by the jackmechanisms 184 and 185 against the roof and lloor. Also, by ventingfluid from the abutment jack 201 while fluid remains under pressure inthe jack 184, the jack 201 may be moved, in preparation for a newfeeding movement of the roof supporting jacks, lby supplying fluid in anappropriate manner to the cylinder and piston mechanism 207.

It is to be noted that the support jacks 184, 185 and the abutment jack201 are arranged in the central longitudinal vertical plane between thepairs of floor and roof engaging devices.

With reference to the fluid control structure associated with thearrangements of Figs. l and 2, it may be observed that the onlydiierence between this construction and that which was shown in Fig. l0and following Figures of the parent case hereinabove identiiied,consists in the provision of three valves for controlling the supply offluid to three jacks, to wit, 184, 185 and 201. Thus, there are threehousings 215, 216 and 217, each containing a controlling valve, theselatter being respectively numbered 219, 220 and 221, and each being ofthe same character as the controlling valves of said Fig. l0 mentioned,to which reference may be had, and each having similar operatingmechanism. Each of the housings contains a chamber in which its valve ismovable, and each chamber communicates through a port with the passage1011" which corresponds to the passage 101" of said Fig. 10. The valve219 controls the admission of iluid to the jack 184. The valve 221controls the admission of fluid to the jack 185, and the valve 220controls the admission of fluid to the abutment jack 201. As all of theremaining structure, except in mere matters of proportion, isessentially the same as is shown in said Fig. l0 and has been fullydescribed, it is unnecessary to go into further detail other than tostate that through conduit means not shown the chamber within the boss215 communicates with the space below the piston of the jack mechanism184, the chamber within the boss 216 communicates with the space belowthe piston in the cylinder structure 204, and the chamber within theboss 217 communicates with the space below the piston in the cylindermember 187.

In view of what has heretofore been said, no substantial furtherdescription of this embodiment of the invention can be called for.Manipulation of the lever determines which end of the cylinder andpiston mechanism 207 has iluid supplied to it and which end is vented,and all that is required to render this device effective to perform itsdesigned function is to time the admission to the several jacks and tothe cylinder and piston mechanism 207 in a manner which is completelyobvious from what has been previously said.

Figs 5 and 6 show a modification of the structure of Figs. 1 to 4, Fig.6 showing the controlling valve mechanism and Fig. 5 a somewhatdifferent arrangement of the jack mechanisms. Because of the similarityin construction, with that of the form heretofore described the forwardjack mechanism may be identied as 184 and the abutment jack mechanism as201 and the rearward jack mechanism as 185. The abutment jack mechanismy201 and the jack mechanism .184' and the cylinder and piston mechanism267' connecting them are essentially identical (with the correspondingparts in the embodiment of the invention shown'in Figs. 1, 2 and 3. Thechains 193 and 194 are not used, however, to connect the rearward jackmechanism 185' through its roof and oor engaging devices 160' and 176'with the arm mechanisms 177 of the jack 184. Instead, a cylinder andpiston mechanism 355 is provided. This consists of a cylinder 356'havinga forward head 357 pivotally connected as at 353 to a rearwardlyprojecting portion 359 of the cylinder member 204'. Within the bore ofthe cylinder and piston mechanism 355 is a suitably packed piston 360having a piston rod 361 of rugged construction and rigidly connected at362 to-the member 18S of the jack device 185'. Suitable connections 365and 366 are provided for the delivery of uid to and the venting of liuidfrom the opposite ends of the cylinder 356, and a connection 367 isprovided for the supply of uid to and its release from the jack device185', such connection corresponding to the bottom connection for thejack 185 of Figs. 2 and 3. It will be understood that by increasing thelength ofthe rearward members 160' and 176' and locating the pistons 360in the rearward ends of their cylinders when the members 169' and 160(and the members 176' and 176') are close together, another mode ofWalking could be provided, in that the front and rear jacks could thenboth be advanced while the abutment jack is stationary, instead ofadvancing the front jack, advancing the abutment jack, and thenadvancing the rear jack.

lt will be observed that tipping of the jack device 184' is impossiblebecause its cylinder and the cylinder of the abutment jack 201' areprevented from moving out of parallelism. Collapse, through tiltingmovement, of the jack device 185' is prevented by reason of itsconnection through the cylinder and piston mechanism 355 to the base ofthe jack 201. It will be evident that if, through pressure to which themine iioor is subjected, there should be a tendency for the oor to beforced upward slightly in its portion beneath the jack device 185', thiswill be possible, Without disturbing anything, because of the pivotalconnection between the jack 185' and the abutment jack 201', for suchconnection permits the jack 185' to be moved out of a positionsubstantially perpendicular to themine bottom. This structure thereforepossesses certain advantages in simplicity over the construction ofFigs. 1, 2 and 3.

The valve mechanism of Figure 6 does not need detailed description.Manually controlled valve mechanisms 371, 372 and 373, with in-builtrelief valves, are provided for controlling the admission of liuid tothe jack device 184', the abutment jack device 201', and the jack device185'. These control the communication of the jacks which theyrespectively control with a fluid supply connection 101m. In addition tothe valve device for controlling the supply of fluid to the cylinder andpiston mechanism 267', which valve device corresponds to the control forthe cylinder and piston mechanism 207 shown in Fig. 4, and whichtherefore will not need further description, there is provided anothervalve device 375 of the two-spool type for controlling communication ofthe connections or conduits 365 and 366 with a passage 376 supplied withhydraulic tiuid under pressure, and with exhaust passages 377, 377, theenduits 365 and 366 cornmunicating with ports 378 and 379 openingthrough the wall of a chamber 38@ in which the valve device 375 isreciprocable by a suitable manual control lever mechanism 381.Thepresent modified form of the invention and its mode of operation andcontrol will require no further description inview of the generalsimilarities to structures of Figs. l to 4.

While there are in this application speciically described two formswhich the invention may assume in practice, it will be understood thatthese forms of the same are shown ,-for purposes of illustration, andthat the invention may ff Patent is:

-1. In a jack mechanism, a plurality of spaced roof supporting jacksincluding a first and a second roof `supporting jack and an abutmentjack located between said first and second roof supporting jacks, acylinder Vand piston mechanism comprising a telescopically arrangedcylinder and piston with a piston rod, said cylinder rigidly connectedto the iirst of said roof supporting jacks and said piston rigidlyconnected to said abutment jack, and a second cylinder and pistonmechanism comprising a telescopically arranged cylinder and piston witha piston rod, said latter cylinder pivotally connected to said abutmentjack and the piston rod of said second cylinder and piston mechanismrigidly connected to the second roof supporting jack.

2. In a jack mechanism, a plurality of spaced roof supporting jacksincluding a first and a second roof supporting jack and anabutment jacklocated between said iirst and second roof supporting jacks, twocylinder and piston mechanisms, each comprising cylinder and piston rodelements, saidelements of one of said cylinder and piston mechanismsrigidly connected to the first of said roofl supporting jacks and toVsaid abutment jack, and said elements of y'said other cylinder andpiston mechanism one rigidly connected to lthe second of said roofsupporting jacksv and the other connectedon a horizontal axis-by pivotalconnecting means to said abutment jack.

3. In a jack mechanism, a plurality of lspaced roof supporting jacksincluding a first and a second roof supporting jack and an abutmentjack, a cylinder and piston mechanism having a cylinder rigidlyconnected to one of said roof supporting jacks and a piston rod rigidlyconnected to said abutment jack, and means connecting the second to theiirst of said roof supporting jacks for movement of the second with thefirst independently of said Vabutment jack.

4. In a, jack mechanism, a plurality of spaced roof supporting, jacksincludinga first and a second roof supporting jack andV an, abutmentjack located between said iirst and Second roof supporting jacks, Vacylinder and piston mechanism having a cylinder rigidly connected to oneof said roof4 supporting jacks and a piston rod rigidly connected yto saidabutment jack, and means connecting Vthe second to the prst ofsaidroof supporting jacks for movement of the second4 with the rst includingexible tie elements.

5. In a jack mechanism, a plurality of spaced roof supporting jacksincluding a iirst anda second roof supporting jack and an abutment jacklocated between said first and lsecond roof supporting jacks, a cylinderand piston mechanism having a cylinder rigidly connected to one of saidroof Asupporting jacks and a piston rod rigidly connected to saidabutment jack, means connecting the secondl to the iirst of said. roofsupporting yjacks for movement .of the second with the iirst includingilexible tie elements, and means .for limiting the minimum distanceapart of said roof supporting jacks.

6. In a jack mechanism, afplurality of spaced roof supporting jacks andan intermediate abutment jack, said roof supporting jacks eachcomprising endless tread type iioor and roof engaging elements and crossarms con` necting the same, a cylinder andjpiston vmechanism foreifecting advance of one of `said roof supporting jacks and having acylinder rigidly connected to said one of said roof supporting jacksanda piston rod rigidly connected to Saidabutment jack, means foroperatively connecting the second of said roof supporting jacks formovement with the iirst including flexible tie .elements extendingbetween said cross arms, and. abutment means carried by theadjacent endsof said-floor and roof en- 9 gaging elements for limiting the minimumdistance apart of said roof supporting jacks.

7. A mine roof supporting jack mechanism, comprising upper and lowermine oor and roof engaging devices, each device including a supportproviding a guideway and an endless tread guided for free circulation inan orbital path along said guideway thereby to provide movable floor androof engaging surfaces of large area, an upright extensible jack deviceconnected between said floor and roof engaging devices for adjusting thelatter in supporting relation between the oor and roof, and a poweroperated device connected to said upright jack device vfor moving thelatter and said floor and roof engaging devices horizontally while saidfloor `and roof engaging devices are maintained in supporting relationwith the oor and roof, said endless .treads circulating freely in theirguideways as said jack device and said oor and roof engaging devices aremoved horizontally as aforesaid.

8. A mine roof supporting jack mechanism, a front jack device, a rearjack device, each of said jack devices having upper and lower mine floorand roof engaging means, each of which includes a support providing aguideway and an endless tread guided for free orbital movement lalongsaid guideway thereby to provide a large movable contact area, anabutment jack located between said front and rear jack devices, poweroperated means between said front and rear jack devices and saidabutment for moving the said front and rear jack devices step by step ina horizontal direction while said front and rear jack devices aremaintained in supporting relation with the mine roof, said endlesstreads of said floor and roof engaging means circulating freely in theirguideways as said front and rear jack devices and said floor and roofengaging means are moved horizontally as aforesaid.

9. In a mine roof supporting jack mechanism, a pair of mine oorsupported endless tread equipped bases, a cross frame extending betweensaid bases and provided with pivotal connecting means therewith forrocking movement of said bases in vertical planes relative to said crossframe, a cylinder and piston type hydraulic jack device supported onsaid cross frame, and, supported on said jack device for engagement withthe mine roof, a further pair of endless thread equipped frames, atransverse frame provided with pivotal connecting means at the endsthereof with said last mentioned frames for rocking movement of saidlast mentioned frames in vertical planes relative to said transverseframe, and a universal ball type mounting for said transverse frame onthe top of said jack device.

l0. In a mine roof supporting jack mechanism, a pair of mine oorsupported endless tread bases, a frame extending between said bases andprovided with pivotal connecting means therewith substantially midway ofthe length thereof for rocking movement of said bases in vertical planesrelative to said cross frame, a cylinder and piston type hydraulic jackdevice supported on said frame, and, a pair of endless tread equippedframes supported on said jack device for engagement with the mine roofby a transverse frame provided with pivotal connecting means at the endsthereof with said last mentioned frames to permit rocking movement ofsaid last mentioned frames in vertical planes relative to saidtransverse frame, and a universal ball type mounting for said transverseframe on the top of said jack mechanism, said endless tread equippedframes projecting forwardly a substantial distance beyond the forwardends of said iioor supported bases.

1l. In a mine roof supporting jack mechanism, front and back pairs ofcarriages adapted for endless tread movement over the mine bottom,hydraulic extensible jack devices supported on said carriages adjacenttheir midpoints, pairs of roof engaging carriages supported on the upperends of said jack devices and movable into engagement with a mine roof,means for eiecting advance of one of said pairs of carriages includingan extensible oor and roof engaging jack and an extensible andcollapsible cylinder and piston mechanism operatively connected to oneof said rst mentioned jacks, and means operatively connecting thecarriages of at yleast one of salid pairs with each other so thatadvance of one of said pairs will effect advance of the other.

l2. In a mine roof supporting jack mechanism, a mine roof engaging meansand a floor engaging means having rolling contact respectively |with theoor and roof, an upright jack device arranged between and operativelyconnected to said roof engaging means and said oor engaging means formaintaining said roof engaging means and said oor engaging means inrespective oor engagement and roof supporting position, and anextensible jack device selectively fixed lto -said roof and said oor byanchor jack means for moving said upright jack device relative to saidroof and said floor to roll sa-id oor and roof engaging means along theroof and floor while remaining in supporting engagement with the roofand the floor.

13. A mine roof supporting mechanism comprising, a plurality of spacedroof supporting means having a first and a second roof supporting meanswith an anchoring means located therebetween, a telescopic mechanismhaving one portion rigidly connected to the first of said roofsupporting means and another portion rigidly connected to said anchoringmeans, and a second telescopic mechanism having one portion pivotallyconnected to said anchoring means and another portion rigidly connectedto the second roof supporting means.

14. A mine roof supporting mechanism comprising, upper and lower mineoor and roof engaging devices each device including a support providinga guideway for supporting means which circulate freely in an orbitalpath along said guideway to provide movable floor and roof engagingsurfaces of large area, an upright extensible device connected betweensaid floor and roof engaging devices for adjusting the latter insupporting relation between the floor and roof, a power operated deviceconnected to said upright extensible device for moving the latter andsaid oor and roof engaging devices horizontally While said door and roofengaging devices are maintained in supporting relation with the floorand roof, and said supporting means circulating freely 4in theirguideways as said extensible device and said oor and roof engagingdevices are moved horizontally as aforesaid.

15. In a mine roof supporting mechanism, a plurality of spaced roofsupporting devices including a firs-t and a second extensible roofsupporting means and an extensible abutment means, a telescopicmechanism having one portion rigidly connected to one of said roofsupporting means and another portion rigidly connected to said abutmentmeans, and means connecting the second to the irst of said roofsupporting means for movement of the second with the first independentlyof said abutment means.

References Cited in the le of this patent UNITED STATES PATENTS1,450,603 Morgan Apr. 3, 1923 1,588,987 OToole June l5, 1926 1,704,866Morgan Mar. 12, 1929 2,420,755 Mavor May 20, 1947 2,496,694 Brown Feb.7, 1950 FOREIGN PATENTS 695,818 Germany Sept. 3, 1940

